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T^reai^iiir  of  tiw* 

DECS  1912 

REPRINTED  FROM  -A^jriciiltTaral 

ORIGINAL  COMMUNICATIONS,   EIGHTH   INTERNATI@^IJeo:# 
CONGRESS  OF  APPLIED  CHEMISTRY.         Vol.  XV— Page  51.     '"' 

A  STUDY  OF  SOIL  POTASSIUM 

Bt  B.  E.  Cubry  and  T.  O.  Smith 

Durham,  N.  H. 

Until  recent  years  the  theory  of  soil  fertilization  has  rested 
almost  entirely  upon  the  practice  of  adding  plant  food  or  amend- 
ments to  the  soil  in  the  form  of  fertilizers  and  manures  for  the  pur- 
pose of  increasing  production.  In  practice  the  ultimate  aim  is 
to  obtain  an  increased  production  at  a  profit.  With  our  present 
knowledge  of  soil  management,  tillage,  and  fertilization  it  is  a 
simple  proposition  to  increase  yields  but  it  is  not  a  simple  prop- 
osition to  secure  profitable  increased  yields.  It  is  doubtful  from 
a  practical  point  of  view  whether  the  maximum  yield  is  the  most 
profitable. 

The  practice  of  applying  fertilizers  is  followed  because  the 
amount  of  plant  food  in  the  soil  is  considered  insufficient  or 
unavailable  for  the  needs  of  the  crop.  For  special  cases  as  in 
market  gardening  and  greenhouse  culture  where  high-priced  crops 
are  grown  the  relatively  small  cost  of  fertilizers  becomes  almost 
negligible.  In  other  crops  such  as  the  average  farmer  grows  the 
difference  of  a  few  dollars  makes  the  difference  between  profit 
and  loss  in  an  operation  on  an  acre.  The  aggregate  of  values  of 
farm  crops  is  largely  derived  from  the  ordinary  crops  grown  under 
ordinary  conditions. 

In  New  Hampshire  one  of  the  large  cash  crops  is  hay.  The 
farms  have  generally  been  allowed  to  run  down  and  become  unpro- 
ductive. The  soil  is  apparently  as  good  as  it  ever  was  but  through 
neglect  production  has  decreased.  A  larger  acreage  is  devoted  to 
grass  than  to  any  other  crop.  This  condition  has  become  estab- 
lished through  the  natural  adaptibility  of  the  soil  to  grass  culture 
and  through  certain  economic  factors  due  to  location  and  labor 
problems.  The  heavy  horse  and  ox  power  once  so  common  on 
New  Hampshire  farms  is  now  a  condition  of  the  past.  Partly 
because  of  this  the  land  does  not  get  the  cultivation  it  once  had. 

61 


52  Original  Communications:  Eighth  International       [vol. 

Commercial  fertilizers  have  in  part  been  substituted  for  tillage 
in  order  to  maintain  production  under  conditions  of  lessened 
tillage. 

A  good  many  general  observations  lead  one  to  believe  that  the 
present  method  of  using  commercial  fertilizers  in  the  production 
of  hay  is  often  unprofitable.  There  seems  to  be  very  little  doubt 
that  in  the  common  use  of  fertilizers  a  very  large  proportion  of 
the  plant  food  added  is  never  converted  into  profitable  plant 
production.  It  is  doubtful  if  the  use  of  commercial  fertilizers 
can  long  be  substituted  for  tillage.  There  are  other  important 
soil  and  plant  growth  factors  which  enter  into  profitable  produc- 
tion and  which  cannot  be  eliminated  by  the  use  of  fertilizers  alone. 

The  soils  of  New  Hampshire  are  extremely  varied  in  charac- 
ter and  are  for  the  most  part  of  granitic  origin.  Almost  any  type 
may  be  found  between  the  limits  of  sand  and  pure  boulder  clay. 
However,  the  sands  in  many  instances  seem  to  be  rich  in  f eld- 
spathic  and  other  minerals.  Many  of  the  types  have  been  con- 
siderably washed  while  others  seem  to  have  been  formed  in  place. 
Areas  of  limestone  soil  are  very  limited  and  are  found  in  only  a  few 
sections. 

In  connection  with  the  use  of  commerical  fertilizers  in  the 
production  of  grass  some  very  interesting  facts  have  been  found. 
Many  of  the  grass  fertilizers  carry  a  large  amount  of  potassium. 
Also  the  tillable  soils  are  on  the  average  very  rich  in  potassium. 
Those  soils  which  are  relatively  poor  in  potassium  contain  large 
amounts  in  the  aggregate.  Some  of  the  boulder  clay  soils  con- 
tain as  high  as  3f  %  K2O.  Assuming  that  an  acre  foot  of  soil 
weighs  three  million  pounds,  such  a  soil  would  contain  fifty-two 
and  one-half  tons  of  K2O  per  acre.  Some  of  the  medium  clay 
soils  carry  about  2%  K2O.  while  the  light  soils  carry  still  less. 
Some  very  sandy  soils  have  been  found  which  contain  as  much  as 
1%  K2O.  Such  soils  carry  a  considerable  amount  of  mineral  in 
connection  with  the  sand. 

With  these  large  quantities  of  potassium  present  in  the  soil 
there  came  the  question  of  the  use  of  potassium  in  commercial 
fertilizers.  Is  it  not  reasonable  to  think  that  the  soil  under  proper 
tillage  conditions  could  supply  enough  potassium  for  the  needs 
of  the  crop  without  the  addition  of  potassium  from  artificial 


xv]  Congress  of  Applied  Chemistry  53 

sources?  It  is  a  remarkable  fact  that  where  potassium  is  added 
in  comparatively  large  quantities  as  a  fertilizer  constituent  that 
that  amount  is  very  insignificant  when  compared  with  the  amount 
of  potassium  present  in  the  soil  under  natural  conditions.  To 
illustrate :  sixty  pounds  of  K2O  is  higher  than  the  average  applica- 
tion per  acre.  In  a  soil  which  carries  2%  K2O  the  amount  per 
acre  foot  aggregates  thirty  tons.  In  comparison  with  sixty 
thousand  pounds,  siTjty  becomes  a  very  small  quantity:  under 
such  conditions  one  pound  is  added  to  one  thousand  pounds 
already  present. 

In  this  connection  it  is  interesting  to  note  that  the  soil  very 
rapidly  renders  the  applied  potassium  insoluble.  For  instance, 
when  dilute  solutions  containing  potassium  salts  are  percolated 
through  columns  of  soils  the  potassium  is  removed  from  solution 
and  changed  into  a  comparatively  insoluble  form.  If  the  salt 
is  the  nitrate,  chloride,  or  sulphate  the  acid  radical  remains  in 
solution  as  the  acid  radical  of  some  new  salt.  When  potassium  is 
percolated  through  as  at  phosphate  both  the  base  and  acid  radicals 
are  removed  from  solution  and  no  new  salt  appears  in  the  percol- 
ate as  in  the  first  inst-ginces. 

The  same  conditions?  hold  when  potassium  salts  come  in  con- 
tact with  the  soil  in  otlier  ways.  In  order  to  show  these  reactions 
five  soils  fairly  reprfjs-entative  of  the  different  types  found  in 
New  Hampshire  were  selected.    An  analysis  of  these  soils  follows : 


54 


Original  Communications:  Eighth  International       [vol. 


Table  I 

Sofl  No. 

1 

2 

3 

4 

5 

Loss  on  Ignition 

2.660 

3 
5.33 

5.830 

4.905 

7.260 

Moisture 

.770 

1.419 

0.516 

.908 

1.681 

Si02 

81.050 

74.090 

72.020 

71.850 

62.340 

P,Oa 

.070 

.084 

.073 

.085 

.089 

FezOs 

1.448 

2.856 

2.896 

2.688 

3.428 

AI2O3 

9.017 

12.195 

13.446 

14.702 

18.638 

CaO 

.756 

.722 

.764 

.806 

.956 

K2O 

1.630 

1.730 

1.910 

2.470 

2.990 

N 

.081 

.186 

.290 

.148 

.257 

Total 

97.482 

98.615 

98.745 

98.462 

97.609 

Na,  Mg,  etc.,  not  deter- 

mined. 

2.518 

1.385 

1.255 

1.538 

2.391 

Sample  No.  1  is  a  light  sandy  soil,  No.  2,  a  light  clay  loam, 
No.  3  a  sandy  loam,  No.  4,  a  heavy  clay  loam,  and  No.  5  a  heavy 
boulder  clay. 

Known  amounts  of  potassium  chloride  in  solution  were  added 
to  these  soils  and  the  moisture  content  brought  up  to  twenty 
per  cent,  by  the  addition  of  water.  The  samples  were  thoroughly 
mixed,  placed  in  sealed  jars,  and  allowed  to  stand  for  several 
weeks.  They  were  then  shaken  with  water  and  the  amount  of 
soluble  potassium  determined  by  the  chloroplatinate  method. 


XV 


Congress  of  Applied  Chemistry 


55 


The  results  follow: 


Table  II 


No.  of  Soil 

Grams  K2O  as 

K  CI  per  Kg. 

soil 

Total 
grams  K2O 
recovered 

Total  grams 

K2O  retained  in 

the  soil 

1 

.9354 

.7012 

.2342 

.6236 

.4471 

.1765 

.3118 

.2024 

.1094 

.1559 

.0072 

.0587 

2 

.9354 

.6173 

.3181 

.6236 

.3872 

.2364 

.3118 

.1871 

.1237 

.1559 

.0841 

.0718 

3 

.9354 

.5517 

.3837 

.6236 

.3460 

.2776 

.3118 

.1724 

.1394 

.1559 

.0709 

.0850 

4 

.9354 

.4400 

.4954 

.6236 

.3101 

.3135 

.3118 

.1240 

.1878 

.1559 

.0561 

.0998 

5 

.9354 

.3243 

.6111 

.6236 

.2712 

.3524 

.3118 

.0779 

.2339 

.1559 

.0437 

.1122 

The  table  shows  that  large  amounts  of  potassium  are  taken  up 
and  held  by  the  soils.  Also,  that  the  amount  of  potassium  so  held 
increases  with  increase  in  the  clay  content  of  the  soil. 


56 


Original  Communications:  Eighth  International       [vol. 


If  di-potassium  phosphate  is  substituted  for  potassium  chloride 
under  the  above  conditions  the  same  results  are  observed  as  is 
shown  in  the  following  table : 

Table  III 


No.  of  Son 

Grams  K2O  as 

K2HPO4  per 

Kg.  of  soil 

Total  grams 
K2O  recovered 

Total  grams 

K2O  retained 

in  the  soil 

1 

2 
3 
4 
5 

3.1840 
3.1840 
3.1840 
3.1840 
3.1840 

1.6238 

.7378 
.4458 
.7472 
.5520 

1.5602 
2.4462 
2.7382 
2.4368 
2.6320 

A  further  examination  of  the  water  extract  of  the  soil  treated 
with  potassium  chloride  shows  that  the  solubility  of  the  acid 
radical  is  not  affected  by  the  soil.  All  the  chloride  appears  in  the 
solution  as  potassium  chloride  and  as  the  acid  radical  of  a  new 
salt.  The  new  salt  or  salts  are  chiefly  chlorides  of  calcium  and 
magnesium.  If  the  acid  radical  is  the  sulphate  or  nitrate  the  same 
conditions  of  solubility  occur.  A  possible  exception  is  the  case 
where  more  calcium  sulphate  is  formed  than  can  dissolve  in  the 
given  volume  of  water. 

Salts  of  iron  and  aluminum  must  in  some  cases  be  formed  in 
the  process  of  these  reactions.  Their  rare  appearance  in  the 
solution  is  probably  due  to  alkalinity  of  the  water  extract  which 
in  many  instances  is  sufficient  to  cause  these  salts  to  hydrolyze 
and  the  bases  to  reprecipitate. 


XV 


'  Congress  of  Applied  Chemistry 


57 


Different  conditions  of  solubility  are  observed  in  the  case  of  the 
phosphates.  The  extent  to  which  they  are  taken  from  solution 
and  retained  by  the  soil  is  shown  in  the  following  table : 

Table  IV 


No.  of  Soil 

Grams  P2O6  as 

K2HPO4  per 

Kg.  of  soil 

Total  grams 
P2O5  recovered 

Total  grams 

P2O5  retained 

in  the  soil 

1 

2.4000 

1.1985 

1.2015 

2 

2.4000 

.4806 

1.9194 

3 

2.4000 

.0846 

2.3154 

4 

2.4000 

.8355 

1.5645 

5 

2.4000 

.5553 

1.8447 

When  soils  react  with  potassium  chloride,  nitrate,  etc.,  the 
reaction  must  be  chemical  because  the  amounts  of  new  salts 
which  appear  in  the  water  extract  are  equivalent  to  the  amount 
of  potassium  removed.  When  soils  react  with  potassium  phos- 
phate both  the  base  and  acid  radical  are  removed  from  solution. 
No  new  salts  appear  in  solution  and  the  water  extract  gives  no 
evidence  of  the  nature  of  the  reaction.  By  analogy,  however,  the 
reaction  must  be  chemical.  When  potassium  exchanges  places 
with  calcium  and  magnesium  these  in  turn  form  phosphates  which 
have  a  very  low  solubility  and  do  not  appear  in  the  solution. 
This  is  further  substantiated  by  the  fact  that  where  large  amounts 
of  calcium  sulphate  are  formed  not  all  of  the  acid  radical  appears 
in  solution. 

At  present  there  are  no  data  at  hand  which  show  the  relation 
between  bacterial  activities  in  the  soil  in  New  England  and  in 
other  sections.  The  probabilities  are  that  such  action  is  com- 
paratively small  and  that  the  rate  of  activity  of  bacterial  action 
increases  with  increase  of  temperature.  Plant  growth  is  greatly 
affected  by  change  in  temperature.  Bacterial  activities  undoubt- 
edly are  affected  by  temperature  changes  in  much  the  same  way. 
This  may  account  in  part  for  the  slow  nitrification  of  the  organic 
matter  in  the  soil  and  afford  an  explanation  why  active  nitrogen- 


58  Original  Communications :  Eighth  International       [vol. 

ous  fertilizers  are  so  uniformly  effective.  The  organic  matter  in 
the  soils  of  old  grass  fields  nitrifies  slowly  also  because  of  lack  of 
tillage  and  consequent  poor  aeration.  The  field  of  soil  bacteriol- 
ogy is  still  almost  untouched  and  affords  some  very  interesting 
sources  for  speculation  in  the  problems  of  soil  fertility  under  these 
conditions. 

In  order  to  secure  as  much  information  as  possible  about  the 
potassium  in  these  soils  both  laboratory  and  field  observations, 
have  been  made.  It  has  been  shown  in  a  preceeding  table  how  the 
soil  behaves  toward  potassium  salts  when  applied  as  soluble 
fertilizer  constituents.  The  amount  of  water-soluble  potassium 
in  many  different  samples  of  soil  has  been  determined  to  show  if 
possible  whether  there  is  any  definite  relation  between  the  total 
potassium  content  of  the  soil  and  the  amount  of  water-soluble 
potassium  in  the  same  soil.  Such  a  relation  cannot  be  established 
with  any  satisfactory  assurance  because  it  has  not  been  possible 
to  secure  soils  which  differ  only  as  regards  the  total  amount  of 
potassium. 

The  total  amount  of  potassium  is  usually  in  proportion  to  the 
amount  of  clay  in  the  soil.  The  amount  of  clay  has  considerable 
effect  on  the  nature  of  the  organic  matter.  The  amount  and 
nature  of  organic  matter  apparently  affects  the  solubility  of 
potassium  and  other  mineral  constituents;  also,  some  soils  carry  a 
large  portion  of  their  potassium  in  the  form  of  minerals.  This  is 
particularly  true  of  the  sandy  soils.  The  solubility  of  potassium 
in  mineral  form  must  be  different  from  that  in  the  form  of  clay. 
This  must  be  true  because  of  the  influence  of  the  clay  itself.  Also 
the  past  treatment  of  the  soil  may  influence  the  solubility  of 
potassium  depending  upon  cultivation  and  whether  or  not  com- 
mercial fertilizers  have  been  used. 


XV 


Congress  of  Applied  Chemistry 


59 


The  solubility  of  potassium  in  pure  ground  feldspar  for  instance 
is  very  different  depending  on  whether  the  solvent  consists  of  pure 
water,  water  carrying  calcium  hydroxide,  or  such  salts  as  sodium 
nitrate,  calcium  sulphate,  etc.,  and  whether  the  mineral  is  pure 
or  mixed  with  clay.  These  facts  are  shown  by  data  in  the  follow- 
ing tables: 


Table  V 


Reagent 
added 

Amt.  of  reagent 
added  in  grams 

cc 
water 

Amount  of  K2O 
liberated  in  grms. 

Aver- 
age 

Amount  of 
K2O  liberat- 
ed by  action 
of  reagent 

0 

0 

180 

. 0064  1 

0 

0 

.0069  \ 

.0067 

0 

0 

0 

.0070 

CaO 

1 

.OI22I 

CaO 

2 

.0156  \ 

.0149 

.0082 

CaO 

2 

.0168^ 

CaS04 

1 

. 0076  1 

CaS04 

2 

.0080  \ 

.0091 

.0024 

CaS04 

3 

.0118 

J 

NaNOs 
NaNOs 

1 
2 

.0120  1 
.0121/ 

.0120 

.0053 

(NH4)2S04 

(NH4).S04 

1 

2 

.OI20I 
.0132/ 

.0126 

.0059 

Na^COs 

Na,C03 

1 
2 

. 0096  1 
.0109/ 

.0103 

.0036 

Na2HP04 
Na2HP04 

1 

2 

.0109  1 
. 0087  / 

.0107 

.0040 

60 


Original  Communications:  Eighth  International       [vol. 


Table  V  shows  the  amount  of  potassium  going  into  solution 
in  a  given  volume  of  water  upon  stirring  the  feldspar  with  some  of 
the  more  common  fertilizer  constituents.  Figures  showing  the 
solubility  of  potassium  when  feldspar  is  stirred  with  clay  and 
calcium  oxide  follow: 

Table  VI 


Bottle 

Grams 
Feldspar 

Grams 
Clay 

Gramn 
CaO. 

cc 
water 

Soluble  K,0 
in  grams 

1 

0 

25 

0.0 

180 

.0014 

2 

0 

25 

2. 

180 

.0011 

3 

30 

25 

1. 

180 

.0072 

4 

30 

25 

2. 

180 

.0062 

5 

30 

0 

0. 

180 

.0067 

6 

30 

0 

0. 

180 

.0072 

7 

30 

0 

1. 

180 

.0151 

8 

30 

0 

2. 

180 

.0158 

The  data  in  Table  V  and  Table  VI  were  obtained  by  placing  the 
different  combinations  in  a  thermostat  at  room  temperature  and 
stirring  until  there  was  no  further  action. 

These  data  show  conditions  which  may  be  met  with  in  soil 
studies  and  why  it  is  difficult  to  eliminate  them  when  making 
comparisons.  The  mineral  feldspar  has  a  certain  solubility  as 
regards  the  potassium  when  the  solvent  is  pure  water.  The 
addition  of  calcium  oxide,  sodium  nitrate  and  other  salts  increases 
the  solubility  very  greatly.  The  presence  of  clay  decreases  this 
effect.  All  soils  except  the  sands  contain  some  clay,  therefore  the 
solubility  of  the  minerals  in  the  soil  is  affected  by  the  clay  and  is 
different  from  what  would  be  expected  from  the  pure  mineral. 
At  present,  it  has  not  been  determined  whether  the  clay  reduces 
the  effect  of  the  solvent  or  whether  the  effect  is  on  the  potassium 
after  it  is  acted  upon  by  the  solvent. 

The  prehminary  part  of  this  work  was  begun  by  looking  into 
the  field  conditions  to  determine  if  possible  whether  anything 


xv]  Congress  of  Applied  Chemistry  61 

could  be  found  from  this  point  of  attack.  A  series  of  plots  were 
fertilized  with  fairly  heavy  amounts  of  nitrogen  in  nitrate  of  soda, 
phosphoric  acid  in  acid  phosphate,  and  potassium  in  the  form  of 
sulphate  and  chloride.  These  plots  have  been  under  observation 
for  the  past  five  years.  To  date,  but  little  information  has  been 
obtained  from  these  plots  excepting  that  the  fertilizers  disappear 
very  rapidly  after  they  are  applied.  It  is  an  easy  matter  to  find 
the  nitrate  and  ammonium  salts  for  sometime  after  they  are 
applied  but  for  all  practical  purposes  it  is  safe  to  say  that  the 
potassium  and  phosphoric  acid  disappear  from  soluble  forms  after 
the  first  good  rainfall  and  in  an  ordinary  application  they  cannot 
be  found  by  chemical  methods  now  in  use.  This  is  in  harmony 
with  the  results  obtained  in  the  experiments  which  have  already 
been  discussed  and  which  show  the  chemical  reaction  which  takes 
place  between  soils  and  potassium  salts.  Like  the  sulfate  and 
chloride  the  nitrate  radical  remains  soluble  until  it  finally  dis- 
appears through  decomposition  or  some  other  destructive  process. 
Because  of  the  chemical  change  which  takes  place  in  the  case  of 
potassium  fertilizers  this  plan  of  attack  could  not  give  any  very 
definite  observations.  Also,  the  relative  amounts  of  soil  and 
fertilizing  elements  were  so  different  that  no  very  satisfactory 
results  could  be  had  in  this  way  to  determine  the  effect  of  the 
fertilizers  on  the  soil  constituents.  On  this  account  the  effects  of 
different  salts  were  studied  under  conditions  which  were  subject 
to  closer  control. 

In  order  to  meet  these  conditions,  solutions  of  various  salts 
of  known  strengths,  were  percolated  through  columns  of  soils, 
the  rate  of  percolation  being  controlled  by  means  of  capillary 
tubes  and  the  height  of  the  water  level  in  the  containing  vessel. 
The  flow  was  adjusted  at  the  rate  of  about  90  c.c.  per  24  hours 
and  maintained  at  that  rate  throughout  the  period  of  observation. 
The  strength  of  the  solutions  was  made  uniform  on  the  basis  of 
the  potassium  equivalent.  The  changes  effected  in  the  passage 
through  the  soil  were  determined  by  studying  the  percolate.  In 
this  way  it  was  possible  to  determine  what  had  been  taken  from 
and  what  added  to  the  original  solution. 

Preliminary  observations  showed  that  all  the  chloride,  nitrate 
and  sulfate  radicals  were  left  in  solution;  for  that  reason  these 


62 


Original  Communications :  Eighth  International        [vol. 


radicals  were  not  considered  further  in  this  discussion.  Except- 
ing phosphates  all  the  solutions  were  destructive  in  respect  to  the 
soil  itself;  but,  in  the  process  of  destruction  new  bases  were  sub- 
stituted for  the  ones  removed. 

The  results  when  potassium  chloride  solution,  0.35  grams  per 
liter,  is  percolated  through  500  gms.  of  soil  are  shown  in  the  fol- 
lowing table : 

Table  VII 


No.  of  Soil 


i 

i 

i>      o 

i 

Q)     O 

M 

9  s  H 

9a§ 

9io 

9a§ 

oa§ 

9a§ 

2-02 

wis 

M2" 
3-5 

M|§ 

III 

a  st3 

ill 

a  ¥-« 

oa5 

oa« 

oa« 

OBS, 

oaa 

oa-3 

1 

.0152 

.0078 

.0050 

.0030 

.0020 

.0018 

.0609 

2 

.0193 

.0096 

.0068 

.0064 

.0040 

.0024 

.0861 

3 

.0205 

.0089 

.0074 

.0061 

.0058 

.0032 

.0928 

4 

.0250 

.0104 

.0080 

.0078 

.0058 

.0028 

.1057 

5 

.0280 

.0139 

.0090 

.0080 

.0067 

.0043 

.1305 

While  lime  and  small  amounts  of  iron  and  aluminum  became 
soluble  a  certain  amount  of  potassium  was  removed  from  solu- 
tion and  retained  in  the  soil.  The  data  show  that  some  of  the 
soils  remove  a  large  part  of  the  potassium  from  the  first  portions 
of  the  percolate.  As  more  solution  is  percolated  through  the  soils 
smaller  quantities  of  potassium  are  retained.  While  these  soils 
contain  naturally  large  amounts  of  potassium  they  remove  addi- 
tional amounts  from  solution.  The  soils  richer  in  clay  and  also 
in  potassium  retain  larger  amounts  than  the  lighter  soils  which 
are  relatively  poorer  in  clay  and  potassium. 

It  has  been  shown  in  Table  VII  that  when  potassium  chloride  is 
percolated  through  columns  of  soil  potassium  is  removed  from 
solution  and  retained  in  the  soil.  The  solubility  of  the  soil  potas- 
sium is  therefore  not  increased  by  such  a  solution.  A  number  of 
solutions  of  different  salts  were  percolated  through  the  soils  to 
determine  what  effect  they  might  have  on  the  solubility  of  the 
soil  potassium.     For  these  experiments  solutions  were  made  of 


XV 


Congress   of  Applied  Chemistry 


63 


sodium  nitrate,  sodium  chloride,  sodium  carbonate  and  acid 
phosphate.  The  strength  of  these  solutions  was  the  same  as  that 
of  the  potassium  chloride  used  in  Table  VII  on  the  basis  of  the 
potassium  equivalent.  The  amount  of  soil  was  also  five  hundred 
grams.  In  order  to  determine  the  effect  of  calcium  carbonate  and 
calcium  sulphate  these  salts  were  mixed  dry  with  the  soil  at  the 
rate  of  1  gram  per  100  grams  of  soil.  Distilled  water  was  perco- 
lated through  these  and  the  percolate  examined  for  potassium. 
The  results  follow : 

Table  VIII 


No.  of  Soil 

Parts  per    million  of 
potassium  in  first  300 
cc.  of  percolate  of  dis- 
tilled  water  through 
500  grams  soil 

Parts  per  million   of 
potassium  in  first  300 
cc.  of  percolate  of  dis- 
tilled  water  through 
500  gms.  soil  plus  1% 
calcium  carbonate 

Parts    per    million   of 
potassium  in  first  300 
cc.  of  percolate  of  dis- 
tilled   water    through 
500   grams,    soil    plus 
1%  calcium  sulfate 

1 

75 

92 

224 

2 

287 

323 

442 

3 

179 

68 

383 

4 

58 

72 

140 

5 

136 

50 

172 

The  data  in  Table  VII  as  well  as  other  observations  made  in 
this  laboratory  show  that  calcium  oxide  and  calcium  carbonate 
do  not  liberate  potassium  from  these  soils.  Some  observations 
have  indicated  a  decreased  solubility.  A  limited  number  of 
observations  with  calcium  sulfate  indicate  that  small  amounts  of 
potassium  are  made  soluble.  These  determinations  have  been 
made  colorimetrically  and  the  evidence  is  not  as  positive  as 
that  obtained  in  the  following  tables  by  the  gravimetric  method. 


64 


Original  Communications :  Eighth  International        [vol. 


Table  IX.     Sodium  Nitrate  Solution 


No.  of  Soil 


.9-s 

•So 

.s-s 

.9  § 

.go 

.S§ 

O  6 

OS 

O  6 

9S| 

o  S 

Og- 

Mo^ 

M82 

MoS 

M§^ 

M^-3 

mO  c3 

,n«i  ^ 

a"o 

S-a  ° 

a':^o 

a  fl « 

a  ja"© 

aSs 

0«a  a 

O^    ft 

2|S 

2  >  o- 

O  d  ft 

03 1>  a 
Ceo 

Table  XI.     Sodium  Carbonate  Solution 


.s  ° 
og 

iCO  oj  O 
I  cor?  fr. 


r^  tn  t^  *rr 


1 

.0029 

.0036 

.0015 

.0007 

.0005 

.  0003 

.0190 

2 

.0027 

.0036 

.0013 

.0006 

.0007 

.0002 

.0182 

3 

.0032 

.0023 

.0020 

.0011 

.0006 

.0004 

.0192 

4 

.0039 

.0037 

.0025 

.0016 

.0014 

.0007 

.0276 

5 

.0051 

.0046 

.0024 

.0018 

.0012 

.0006 

.0314 

Table  X.    Sodium  Chloride  Solution 

' 

!a<» 

•«  o 

a  o 

.B-z 

.ss 

s  ° 

.S§ 

.9*° 

O  6 

o§ 

9§ 

9§- 

o§ 

o§ 

OS 

No.  of  SoU 

a"o 

Ota  ft 

MO  a) 

Mo2 

a"o 

Ota  ft 

a  fl  s 
§  ^  ft 

OS'S 

O  a  ft 

ago 

a  >  2 

O  0)  a 

Grams  K' 
first  3600 
percolate 
(Approx.) 

1 

.0021 

.0017 

.0010 

.0004 

.0005 

.0003 

.0120 

2 

.0017 

.0022 

.0010 

.0005 

.0003 

.0004 

.0122 

3 

.0024 

.0024 

.0009 

.0008 

.0002 

.0004 

.0142 

4 

.0025 

.0026 

.0018 

.0006 

.0008 

.0006 

.0178 

5 

.0042 

.0037 

.0015 

.0017 

.0008 

.0010 

.0258 

No.  of  Soil 


a- 

a"o 

a>« 

a  6 

a  o 

.gs 

•«  o 

06 

OS 

Oci 

9S| 
%2 

O  § 

082 

«oS 

M85 

MoS 

M§S 

M.a  0 

mO    C3 

mO  03 

a"  o 

ItjO 

a""o 

a  s  S3 

a.ja'o 

aSs 

Ota  ft 

S.t5  ti 

O't^  ft 

M 

2^^ 
OS'S 

Oa  ft 

OH  0 

.So 
O  o 


(n  CD  ffj  o 

a'"  o  ft 

s-g  g  ft 
Ota  ao- 


1 

.0019 

.0015 

.0011 

.0005 

.0004 

.0003 

.0114 

2 

.0021 

.0013 

.0008 

.0009 

.0003 

.0004 

.0116 

3 

.0025 

.0020 

.0010 

.0010 

.0004 

.0004 

.0146 

4 

.0022 

.0019 

.0014 

.0007 

.0005 

.0007 

.0148 

5 

.0025 

.0024 

.0022 

. 0018V 

.0008 

.0006 

.0206 

XV] 


Congress  of  Applied  Chemistry 


65 


Table  XII.    Acid  Phosphate  Solution 


No.  of  Soil 

a°o 

.So 

98 

oil 

.s-s 

9§l 

a  d  !3 
OS'S 

d"o 

III 

.8  8 

gSs 

if! 

Co  0 

Grams  KiO  in 
first  3600  cc.  of 
percolate 
(Approx.) 

1 

.0020 

.0026 

.0017 

.0002 

.0004 

.0003 

.0144 

2 

.0014 

.0026 

.0019 

.0003 

.0008 

.0005 

.0150 

3 

.0025 

.0027 

.0021  ; 

.0005 

.0006 

.0004 

.0176 

4 

.0024 

.0041 

.0015 

.0003 

,0010 

.0007 

.0200 

5 

.0043 

.0042 

.0018 

.0005 

.0010 

.0009 

.0254 

Tables  IX,  X,  XI  and  XII  show  that  dilute  solutions  of  sodium 
nitrate,  sodium  chloride,  sodium  carbonate  and  acid  phosphate  in 
contact  with  these  soils  liberate  potassium  in  considerable 
amounts.  The  data  in  Table  XII  was  secured  to  determine  the 
effect  of  commercial  acid  phosphate  in  liberating  potassium.  A 
sample  was  found  which  contained  no  potassium  and  the  soluble 
phosphate  extracted  with  water.  The  free  acid  was  neutralized 
with  lime,  the  solution  filtered  and  standardized. 

As  already  stated  these  observations  could  not  be  obtained 
from  field  work  because  of  the  relatively  small  amounts  of  fer- 
tilizers generally  used.  There  is,  however,  no  reason  to  believe 
that  these  same  reactions  do  not  take  place  under  field  conditions. 
The  solutions  used  in  these  experiments  while  dilute  are  much 
more  concentrated  than  soil  solutions  excepting  under  special 
conditions.  Nitrate  of  soda  and  acid  phosphate  solutions  are 
very  active  in  their  effect  on  potassium.  This  has  a  very  practical 
bearing  in  relation  to  crops  grown  in  connection  with  nitrate  and 
acid  phosphate  fertilizers. 

In  the  field  observations  have  been  made  to  determine  the 
relation  between  potassium  fertilizers  and  the  yield  of  the  crop. 
Potassium  salts  have  been  used  alone  and  also  in  connection  with 
nitrogenous  and  phosphate  constituents.  For  this  work  soils  of 
uniform  character  have  been  selected  and  plots  laid  out  and 
treated  in  various  ways  to  show  the  specific  effect  of  the  potassium 
salts.    The  plots  have  been  placed  on  different  types  of  soil  to 


66  Original  Communications :  Eighth  International       [vol. 

afford  an  opportunity  to  show  how  different  soils  respond  to  the 
same  treatment.  The  fertihzers  have  consisted  of  nitrate  of  soda, 
acid  phosphate,  potassium  sulphate  and  potassium  chloride  and 
have  been  applied  singly  and  in  combinations  as  a  top  dressing 
on  grass  fields.  One  or  more  check  plots  have  received  no  fer- 
tilizers. This  provided  a  means  for  observing  the  value  of  potas- 
sium under  all  ordinary  conditions.  In  general  the  effect  of  a  com- 
bination of  fertihzers  has  not  been  additive.  To  show  the  results 
on  different  types  of  soils  the  yields  on  a  number  of  series  follow. 
The  results  show  average  yields  for  a  period  of  two  or  more  years 
on  the  same  field:  The  following  five  tables  show  the  influence 
of  the  various  fertilizing  constituents  when  applied  as  a  top  dress- 
ing under  ordinary  field  conditions  to  soils  representing  the 
five  types  already  discussed.  Whenever  used  the  fertilizers  were 
apphed  at  the  rate  of  120  lbs.  K2O,  40  lbs.  N,  and  50  lbs.  PaOs 
per  acre. 

The  plots  to  which  these  fertilizers  were  applied  had  received 
no  fertilizers  for  more  than  a  year  and  were  covered  with  a  good 
timothy  sod  from  which,  in  most  cases,  at  least  one  crop  of  grass 
had  been  removed. 

Table  XIII.     Yield  on  a  Sandy  Soil 

Nitrate  of  Soda, 
Nitrate  of  Soda  Nitrate  of  Soda     Muriate  of    Acid  Phosphate 
Muriate  of  and  Acid         and  Muriate      Potash  and        and  Muriate 

Check  Potash  Phosphate  of  Potash      Acid  Phosphate      of  Potash 

1.155        1.155        1.575        1.330  1.120        2.170 

Table  XIV.     Yield  on  a  Light  Sandy  Loam 
.945  .875        1.715        1.890        1.085        2.625 

Table  XV.     Yield  on  a  Light  Clay  Loam 
.931  .805        2.660         2.415  .945        2.975 

Table  XVI.     Yield  on  a  Heavy  Clay  Loam 
1.505  1.330        2.537        3.110        1.910        2.905 

Table  XVII.     Yield  on  a  Heavy  Boulder  Clay 
1.702  1.616        2.079        2.089        1.819         .2140 


xv]  Congress  of  Applied  Chemistry  67 

In  general  the  yields  from  the  different  plots  on  the  various 
types  of  soils  were  uniform  in  a  number  of  respects.  There  is 
considerable  variation  in  the  yields  which  come  from  the  plots  on 
the  different  types  of  soils  but  these  may  be  due  more  to  seasonal 
differences  than  to  productiveness  of  the  soil  itself  or  influence  of 
the  fertilizers. 

The  effect  of  muriate  of  potash  when  used  alone  or  in  connec- 
tion with  acid  phosphate  produced  no  increased  yield  of  hay.  A 
considerable  increase  in  yield  was  produced  when  muriate  of 
potash  was  used  with  nitrate  of  soda.  This  increase,  however,  is 
due  to  the  effect  of  the  nitrate  of  soda.  Some  increase  in  produc- 
tion is  obtained  when  muriate  of  potash  is  used  in  connection  with 
nitrate  of  soda  and  acid  phosphate.  This  increase  is  greatest  on 
the  lighter  soils.  On  heavier  soils  the  potassium  has  very  little 
effect  under  any  conditions. 

The  following  data  show  the  average  yield  obtained  by  the  use 
of  chloride  and  sulphate  of  potassium  on  a  series  of  plots  over  a 
period  of  five  years. 

Table  XVIII.     Compaeative  Yields  for  the  Chloride  and 
Sulphate  of  Potassium 

Check  Sulphate  of  Potassium  Chloride  of  Potassium 

1.565  1.595  1.485 

Potassium  was  applied  at  the  rate  of  90  lbs.  K2O  per  acre.  The 
check  plot  as  shown  in  Table  XVIII  has  produced  more  hay  than 
the  plot  fertilized  with  potassium  chloride.  The  difference  is 
small  but  is  not  an  unusual  observation.  The  sulphate  of  potas- 
sium has  produced  practically  no  increased  yield  during  this 
period. 

A  large  number  of  analyses  have  been  made  to  determine 
whether  the  yield  affects  the  composition  of  the  crop.  Crops  pro- 
ducing both  small  and  large  yields  were  studied  to  determine 
whether  the  amount  of  potassium  removed  was  directly  propor- 
tional to  the  weight  of  the  crop.  With  the  almost  unlimited  and 
inexhaustible  amount  of  potassium  existing  in  the  soil  this 
becomes  a  very  important  consideration.     Samples  of  hay  have 


08 


Original  Communications:  Eighth  International       [vol. 


been  analyzed  from  the  plots  already  discussed  located  on  the 
different  types  of  soils  and  the  amount  of  K2O  removed  per  acre 
calculated.    These  data  follow: 


Table  XIX 

No. 

Yield  per  acre 

Per  cent.  K2O 

Lbs.  K2O 

1 

945 

1.80 

17 

2 

1875 

1.77 

32 

S 

2344 

1.67 

30 

4 

2818 

1.87 

52 

5 

3088 

1.54 

48 

6 

3268 

1.85 

60 

7 

3616 

1.61 

58 

8 

4504 

1.51 

68 

9 

5174 

1.86 

96 

10 

5412 

1.73 

94 

11 

6010 

1.62 

97 

12 

6374 

1.81 

115 

It  is  evident  from  Table  XIX  that  the  percentage  of  potassium 
is  practically  the  same  for  all  samples  of  hay  from  the  unfer- 
tilized plots  regardless  of  the  yield.  While  slight  variations  were 
found  the  general  tendency  has  been  for  the  potassium  to  vary 
directly  with  the  amount  of  hay.  These  results  are  shown 
graphically  in  Fig.  1. 

In  the  figure  the  amount  of  potassium  is  shown  along  the  line 
AB  and  the  yield  of  hay  along  the  line  AC.  The  line  AD  repre- 
sents the  relation  between  the  yield  of  hay  and  quantity  of  KtO 
contained.  The  range  represented  in  this  figure  is  wide  and  in 
the  case  of  the  heavier  crops  the  yield  is  near  a  maximum.  The 
analysis  of  samples  of  hay  grown  on  plots  which  have  received 
potassium  fertilizers  does  not  show  that  they  contain  a  higher 
per  cent,  of  potassium  than  hay  grown  on  unfertilized  plots.  In 
eases  where  the  yield  has  been  increased  by  the  addition  of  nitrate 
of  soda  and  acid  phosphate  the  composition  is  again  fairly  con- 


xv] 


Congress  of  Applied  Chemistry 


stant  showing  that  the  soils  must  have  supplied  relative  amounts 
of  potassium. 


D 


B 

.110 

.too 

T^i.  1 

X 

/ 

£ 

.80 

y 

/ 

5 

/ 

'51 

en 

/  + 

« 
+» 

.60 

O 

X"^ 

a. 

«f- 

X\ 

o 

.IfO 

«/\ 

T3 

J 

r 

/ 

3 

.zo 

/ 

o 

y 

Ol. 

/ 

/" 

/ 

1000 

1 

ICOO       3O0O 

ifOOO 

5000 

-J 

60OO 

1    1               t — 

^   Pounds  of  Hay 


Figure  1 


In  the  light  of  the  information  received  from  the  percolation 
experiments  and  from  the  observations  made  in  field  work  it 
appears  to  be  logical  for  the  yield  of  the  nitrate  of  soda  plots  to 
be  equal  to  those  which  have  been  treated  with  nitrate  of  soda  in 
connection  with  potassium  salts.  From  the  percolation  experi- 
ments it  is  evident  that  where  nitrate  of  soda  is  used,  the  results 
are  produced  by  the  action  of  the  nitrate  of  soda  itself  and  also 
by  the  action  of  the  nitrate  of  soda  on  the  potassium  in  the  soil. 
The  effects  of  nitrate  of  soda,  as  observed  should  therefore  be 
much  the  same  as  would  be  obtained  by  the  use  of  both  nitrate 
of  soda  and  potassium  salts.  In  this  connection  the  percolation 
experiments  indicate  that  common  salt  might  in  some  ways 


70  Original  Communications :  Eighth  International       [vol. 

replace  potassium  salts  in  fertilizers  for  some  soils.  The  same 
might  be  said  of  acid  phosphate. 

Field  observations  show  that  a  large  number  of  our  soils  con- 
tain sufficient  soluble  potassium  to  produce  maximum  yields  of 
grass.  This  appears  to  be  true  whether  the  potassium  is  in  its 
natural  condition  or  whether  it  is  affected  by  salts  which  have 
a  tendency  to  increase  its  solubility. 

From  a  practical  point  of  view  little  encouragement  can  be 
given  to  the  grass  grower  to  use  potassium  fertilizers  on  these  soils. 
The  soils  furnish  sufficient  potassium  to  produce  very  large  crops 
and  hundreds  of  years  would  be  required  to  diminish  the  supply 
materially.  Field  observations  show  that  practically  all  of  the 
potassium  in  fertilizers  produces  no  beneficial  results  and  that  in 
no  case  have  we  found  that  potassium  has  produced  a  profitable 
increase  whether  used  singly  or  in  combination  with  other  fer- 
tilizers. 

Summary 

It  has  been  pointed  out  that : 

1.  A  large  amount  of  potassium  fertilizer  is  not  used  profitably 

at  the  present  time. 

2.  New  Hampshire  soils  are  rich  in  potassium  and  naturally 

adapted  to  the  production  of  hay. 

3.  The  soil  potassium  is  present  in  clay  and  in  mineral  form. 

4.  The  soils  remove  large  quantities  of  potassium  from  solution 

under  both  laboratory  and  field  conditions. 

5.  When  potassium  phosphate  reacts  with  the  soils  no  new 

soluble  salts  appear  in  solution. 

6.  When  other  potassium  salts  react  with  the  soil  new  bases 

do  appear  in  solution. 

7.  Excepting  phosphoric,  the  solubility  of  the  common  acid 

radicals  is  not  affected  by  the  action  of  the  soil. 

8.  The  effect  of  such  salts  as  sodium  chloride,  sodium  nitrate, 

sodium  carbonate  and  acid  phosphate  is  to  greatly  increase 
the  solubility  of  the  soil  potassium. 

9.  The  reaction  between  these  salts  and  the  soil  is  chemical. 


xv]  Congress  of  Applied  Chemistry  71 

10.  Calcium  carbonate,   calcium  sulphate  and  calcium  oxide 

have  practically  no  effect  on  the  solubility  of  soil  potas- 
sium. 

11.  The  feldspar  minerals  have  a  definite  solubility  in  water. 

This  solubility  is  affected  by  lime  and  the  common  salts 
found  in  fertilizers.  The  effect  of  these  is  modified  by  the 
presence  of  clay. 

12.  Field  observations  show  that  potassium  fertilizers  do  not  pro- 

duce increased  yields  of  grass,  particularly  on  clay  soils. 
In  some  combinations  they  are  more  effective  on  the  sandy 
soils,  but  not  profitably  so. 

13.  In  many  cases  nitrate  of  soda  alone  produces  yields  as  good 

as  are  obtained  with  a  combination  of  nitrate  of  soda  and 
potassium  salts.  This  may  be  due  to  the  effect  of  the 
nitrate  of  soda  on  the  soil  potassium. 

14.  The  composition  of  the  hay  shows  that  when  no  potassium 

fertilizers  are  used  the  soil  affords  plenty  of  potassium  for 
the  growth  of  the  crop.    This  is  true  for  large  yields. 

15.  From  a  practical  point  of  view  little  profit  can  be  expected 

from  the  use  of  potassium  fertilizers  for  the  production  of 
hay. 


